You can integrate the sensor directly into Home Assistant via Bluetooth if your system supports Bluetooth. An additional hub from the manufacturer is not absolutely necessary. Home Assistant automatically recognises the sensor via the RuuviTag BLE integration as soon as Bluetooth is activated and functional.
The "Ruuvi Gateway" is actually an optional hub that can improve the range and reliability of sensor transmission by collecting and forwarding data from the sensors. However, it is not absolutely necessary for integration into Home Assistant, but rather an addition for larger or more complex setups.
For Google Home, direct integration without a hub is not provided as standard; an intermediate layer or hub is usually required to integrate the sensor data into Google Home.
The battery in a RuuviTag Pro usually lasts between 12 and 24 months, depending on the operating conditions and ambient temperature. In some cases, the battery can last up to three years if the conditions are optimal.